Final answer:
The beginning of Act 4 in Shakespeare's 'Julius Caesar' signifies a pivotal turn, where the formation of the Second Triumvirate marks a shift towards retribution and power consolidation after Caesar's assassination, paralleling the historical fall of the Roman Republic.
Step-by-step explanation:
In Shakespeare's Julius Caesar, the beginning of Act 4 marks a significant turn in the play. Following the chaos of Caesar's assassination, Act 4 opens with the formation of the Second Triumvirate, comprising Octavian (later Augustus), Antony, and Lepidus. This new alignment of power symbolizes a shift from the idealistic struggle over the future of the Roman Republic towards the dark, pragmatic politics of retribution and consolidation of power. The three leaders are shown dividing the Roman territories among themselves and engaging in the proscription of their enemies, which includes the cold calculation of sacrificing their own kin for political expediency. The emergence of the Second Triumvirate and the ensuing battles mark the decline of the Republic and the rise of the empire, aligning with the historical backdrop of Rome's transformation. The atmosphere at the opening of this act is one of betrayal, political scheming, and the loss of the republic's ideals, setting the stage for the subsequent tragic events of the play.